Restore registers at the head of chains of contained nodes (dotnet#118430)

Fixes dotnet#118377

Author: a74nh

src/coreclr/jit/lsra.cpp

@@ -7665,25 +7665,18 @@ void LinearScan::insertUpperVectorRestore(GenTree*     tree,
     if (tree != nullptr)
     {
         LIR::Use treeUse;
-        GenTree* useNode  = nullptr;
-        bool     foundUse = blockRange.TryGetUse(tree, &treeUse);
-        useNode           = treeUse.User();
+        bool     foundUse;
+        GenTree* useNode = tree;
 
-#ifdef TARGET_ARM64
-        if (refPosition->needsConsecutive && useNode->OperIs(GT_FIELD_LIST))
-        {
-            // The tree node requiring consecutive registers are represented as GT_FIELD_LIST.
-            // When restoring the upper vector, make sure to restore it at the point where
-            // GT_FIELD_LIST is consumed instead where the individual field is consumed, which
-            // will always be at GT_FIELD_LIST creation time. That way, we will restore the
-            // upper vector just before the use of them in the intrinsic.
-            LIR::Use fieldListUse;
-            foundUse = blockRange.TryGetUse(useNode, &fieldListUse);
-            treeUse  = fieldListUse;
+        // Get the use of the node. If the node is contained then the actual use is the containing node
+        // (which may be much later in the LIR). Repeatedly check until there is no contained node.
+        do
+        {
+            foundUse = blockRange.TryGetUse(useNode, &treeUse);
             useNode  = treeUse.User();
-        }
-#endif
-        assert(foundUse);
+            assert(foundUse);
+        } while (useNode->isContained());
+
         JITDUMP("before %d.%s:\n", useNode->gtTreeID, GenTree::OpName(useNode->gtOper));
 
         // We need to insert the restore prior to the use, not (necessarily) immediately after the lclVar.

src/tests/JIT/Regression/JitBlue/Runtime_118377/Runtime_118377.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v3.3 on 2025-08-05 00:20:11
+// Run on Arm64 Linux
+// Seed: 7831934182807398228-vectort,vector64,vector128,armadvsimd,armadvsimdarm64,armaes,armarmbase,armarmbasearm64,armcrc32,armcrc32arm64,armdp,armrdm,armrdmarm64,armsha1,armsha256,armsve,armsve2
+// Reduced from 61.3 KiB to 1.3 KiB in 00:00:54
+// Debug: Outputs <14533768479604701151, 1>
+// Release: Outputs <14533768479604701151, 0>
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Numerics;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
+using Xunit;
+
+public class Runtime_118377
+{
+    public static ulong s_4;
+    public static ulong F0 = 1;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static Vector<ulong> M4()
+    {
+        var vr3 = Sve.CreateWhileLessThanMask64Bit(0, 0);
+        var vr5 = Vector.Create<ulong>(s_4);
+        var vr1 = Sve.CreateBreakPropagateMask(vr3, vr5);
+        var vr7 = Vector.Create<ulong>(0);
+        return Sve.Add(vr1, vr7);
+    }
+
+    [Fact]
+    public static void TestEntryPoint()
+    {
+        if (Sve.IsSupported)
+        {
+            var vr4 = F0;
+            var vr0 = Vector.Create<ulong>(vr4);
+            var vr8 = Vector128.CreateScalar(14533768479604701152UL).AsVector();
+            var vr10 = F0;
+            var vr9 = Vector.Create<ulong>(vr10);
+            var vr6 = Sve.AbsoluteDifference(vr8, vr9);
+            var vr11 = M4();
+            Vector<ulong> var2 = Sve.ConditionalSelect(vr0, vr6, vr11);
+            Console.WriteLine(var2);
+            Assert.Equal(14533768479604701151UL, var2[0]);
+            Assert.Equal(1UL, var2[1]);
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_118377/Runtime_118377.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <!-- Needed for CLRTestEnvironmentVariable -->
+    <RequiresProcessIsolation>true</RequiresProcessIsolation>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+    <NoWarn>$(NoWarn);SYSLIB5003</NoWarn>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+    <CLRTestEnvironmentVariable Include="DOTNET_TieredCompilation" Value="0" />
+    <CLRTestEnvironmentVariable Include="DOTNET_JITMinOpts" Value="0" />
+  </ItemGroup>
+</Project>